The air temperature inside a passenger cabin of a fixed wing or rotor aircraft may fluctuate significantly during flight operations. These temperature fluctuations depend upon physical characteristics of the aircraft in combination with operational and ambient conditions associated with the aircraft while on the ground or in flight.
Among the physical characteristics of an aircraft that can affect cabin air temperature are the extent to which the cabin is thermally insulated, the number and size of windows provided, the proximity of the engines to the cabin, and the composition of the materials employed in the construction of the aircraft. These factors allow heat to enter or escape from the cabin through convective, conductive, and/or radiation processes. These processes, in turn, depend upon operational and ambient conditions associated with the aircraft such as the outside ambient temperature, the altitude of the aircraft, the speed of the aircraft, and the extent of cloud cover when the aircraft is operating above, within, or below clouds.
In order to provide passenger comfort within the cabin, it has been known to incorporate heating and cooling systems into aircraft cabin designs. In a typical cooling system for use in an aircraft cabin, the cooling system comprises a manually adjustable system for circulating ambient air within the cabin, alone or in combination with cool air provided by an air conditioning unit located within the aircraft. In these cooling systems, it is typical for the ambient air to enter the aircraft through an ambient air inlet and to circulate about the cabin through the use of fans or blowers. These fans or blowers may also be used in combination with the air conditioning unit to circulate cool air, or cool air mixed with ambient air, about the cabin.
Adjustment of these prior art cooling systems is strictly manual, in that an operator of this type of cooling system must manually select a combination of system settings that the operator believes will increase passenger comfort. These system settings include the rate at which ambient air is allowed to enter the aircraft, the speed settings of the various circulation fans or blowers, and if an air conditioning unit is used, the rate at which the air conditioner's compressor supplies refrigerant to the air conditioner's evaporator coils.
A drawback to these prior art cooling systems lies in that these systems are unable to automatically compensate for dynamic operational and ambient conditions associated with the aircraft that result in temperature changes within the aircraft cabin. For example, during the operation of a rotorcraft, the ambient temperature surrounding the rotorcraft changes as a function of the altitude of the rotorcraft. In addition, since a rotorcraft typically utilizes large expanses of glass, solar radiation becomes a factor as the rotorcraft operates above cloud cover. These dynamic changes can occur very rapidly since one advantage of a rotorcraft is its vertical maneuverability. Therefore, an operator of a prior art cooling system would have to manually adjust the cooling system's settings as the cabin temperature changes in response to these dynamic changes in the operational and ambient conditions associated with the rotorcraft. These manual adjustments may not necessarily improve passenger comfort, since these dynamic changes can occur at a rate that is faster than the rate at which an operator can input the system setting adjustments and the rate at which the cabin temperature is able to reflect these manual adjustments.
In a typical heating system for an aircraft having a turbine engine, heat is provided to the cabin through a manually adjustable heating system that directs hot bleed air from the turbine engine's compressor into the cabin. Adjustment of the heating system is achieved by manually regulating the flow of bleed air into the cabin with bleed air valves. As with the prior art cooling systems discussed above, the prior art heating systems also strictly rely upon manual adjustments. In addition, as with the prior art cooling systems, the prior art heating systems are unable to automatically compensate for dynamic operational and environmental conditions associated with the aircraft that alter the temperature within the aircraft cabin.
In particular, the power settings of the turbine engine(s) impact the effectiveness of the prior art heating systems. It is known in the art that the temperature and flow rate of bleed air is a function of the power setting of the turbine engine supplying the bleed air. Therefore, for a given set of operational conditions, the temperature and flow rate of the bleed air may be greater or less than the heating needs of the aircraft. In addition, it is known that decreasing the diversion of bleed air from a compressor of a turbine engine increases engine efficiency. Therefore, if it becomes necessary in certain operational situations to increase engine efficiency, the flow of bleed air available for heating purposes will be reduced. Since the prior art heating systems rely on manual adjustment, it becomes very difficult for an operator to properly adjust the system controls in response to dynamic changes in both ambient and operational conditions associated with the aircraft, e.g., changes in bleed air temperature and flow rate.